Transmission system



June 2, 1936.

H. COHN TRANSMISSION SYSTEM Filed Jan. 16, 1934 2 Sheets-Sheet l 89 se g5 1? FE J2": 2 3 5 EE 3 Irwentor: II 060%,

June 2, 1936. H 2,042,652

TRANSMISSION SYSTEM 2 Filed Jan. 16, 1954 2 Sheets-Shqet 2 Patented June2, 1936 UNITED STATES PATENT OFFICE TRANSMISSION SYSTEM Iiugo Cohn, NewYork, N; Y., assignor to Radio Receptor Co. Inc., New York, N. Y., acorporation of New York .The invention relates to av system by whichperiodic signals may be transmitted to various points and also variousprograms of music,

speeches, radio broadcasts and the like may also be transmitted to thesame variouspoints. The system is so arranged that its use for one typeof transmission will not preclude its use for the other type oftransmission.

Without intending to limit the invention, but

for the purpose of clearly disclosing it in a simple manner it may bedescribed as applied to a school system. It will be understood, ofcourse, that the invention is not limited to school systems but may beemployed in whole or in part in other connections such as hospitals,hotels, auditoriums and other installations,

In many schools there is installed a clock associated with. mechanismfor causing signals such as bells or the like in various rooms of theschool 2-0.- to be sounded at appropriate predetermined times. It is apurpose of the present invention to associate with such a system a loudspeaker at each of the school rooms Where the time signal is sounded orat certain selected ones.

2;- be associated with the system a receiver which maybe a microphone ora radio receiver or a phonograph or the like to bring to the systemcertain sounds which are to be delivered through the loud speakers. Theapparatus in each room 30 may be controlled by a switch which may allowthe bell-ringing or signal current to go to it, or which may allow thecurrent from the receiver, which may be referred to as the talkingcurrent, to go to it. There also may be associated with the systemmechanism or switches by which the talking current may be led to theapparatus in all the rooms or in a group or groups of rooms. There -mayalso be provided mechanism or a switch preferably automatic in itsoperation controlled by the program clock for closing the signal circuitfor a short time to sound the signals in proper rooms at the times forwhich the program clock may be set even when the talking circuit is inoperation. This mechanism preferably will be such as not to permanentlyinterrupt the talking circuit but to allow it to continue to operateafter the signal required by the clock has been given.

53 In the accompanying drawings Figure 1 is a diagrammatic showing ofone form of system involving the invention in which the bells or othersignalling devices in the individual rooms are operated by drect currentor by alternating cur- :rent. Fig. 2 is a similar diagrammatic view of aThere may system in which the bells or signalling devices may beoperated by alternating current.

In Figure 1 a source of direct current I0 is indicated for operating thevarious signaling devices, illustrated as bells. This may consist of abattery or any other suitable source. A2 designates generally theapparatus in one room consisting of a signaling device II which may be abell or other suitable mechanism. In parallel with this in the room Allis shown a loud speaker 12. Similarly A3 indicates a room in which is asignaling device i3 in parallel with a loud speaker l4. B2 indicates aroom in which is a signaling device l5 in parallel. with a loud speakerl6 and B3 indicates a room in which is a signaling device I! in parallelwith the loud speaker Hi. It will be understood that the signalingdevices do not operate with the alternating current which operates theloud speakers-and the loud speakers do not operate normally with thedirect current which operates the signaling devices. This is I effectedby suitable selection and installation as is well known in the art. Ifthe signaling system is direct current the loud speaker may click whenthe current is made and when the current is broken, and in somecircumstances may even buzz slightly; if the signaling sytem isalternating current, the loud speaker may buzz more or less loudlydepending upon the frequency but this is negligible and does not impairthe usefulness of the system.

PC indicates a program clockwhich together with the other apparatusabout to be described may be located at any suitable point in theschool.

It may be convenient to place this at some central point such as theoffice of the principal or convenient thereto. As is usual, the programclock is indicated as having a number of ringing circuits marked l, 2,3, 4, 5 and 6' so that different bells or different groups of bells maybe operated on different schedules andthere is provided aninterconnecting board indicated generally by the letter B provided witha plurality of busbars corresponding to the six circuits of the programclock PC. These are so arranged that one or a plurality or all of thesignaling devices in the various rooms may be connected to any one ofthe busbars by plugs, screws, or other means, in the manner well knownin the art. In Fig. 1 the plug AZP is indicated in place as connectingthe apparatus of the room A2 with the busbar associated with station2011 the program clock PC. The plug BZP connects the apparatus in theroom B2 with the busbar associated with the station 2 on the programclockPC. Likewise the apparatus in the rooms A3 and B3 is connected tothe busbar associated with station 3 of the program clock PC by means ofthe plugs A3? and B3B respectively. Apparatus in other rooms (not shown)may be connected to these or other busbars in ways well known in theart. The dotted lines on the program clock PC indicate connections withthe busbars through the program clock to one side of the battery I0. Itwill be understood of course that these connections are normally openbut are closed by the program clock at predetermined times.

Arranged at a suitable place which may be centrally located adjacent theprogram clock PC and away from the rooms are a plurality of controllingswitches one for the apparatus in each room. CA2 indicates a controllingswitch for the apparatus in the room A2. CA3 indicates a controllingswitch for the apparatus in the room A3. CB2 indicates a controllingswitch for the apparatus in the room B2. CB3 indicates a controllingswitch for the apparatus in the room B3. Each of these switchescomprises mechanism for passing current through the loud speaker byconnecting it with the output transformer which is diagrammaticallyindicated at OT.

Associated with each of the busbars on the board B and located atsuitable points which may be adjacent the program clock PC are mastertalking switches which connect the talking circuit to the busbars andthus to the apparatus roe.

in all of the rooms connected to the busbars. MT2 indicates a mastertalking switch associated with busbar 2 and controlling the mastertalking circuit to the apparatus in rooms A2 and B2 both of which areshown connected with the busbar 2. MT3 indicates a master talking switchassociated with the busbar 3 and controlling the master talking circuitwith the apparatus in rooms A3 and B3 both of which are shown connectedwith the busbar 3. If desired these master controlling switches may beso arranged that all or a plurality of them may be thrown together andoperate for a plurality of busbars.

Associated with the program clock contacts for the various busbars areswitches which may automatically close the signaling circuits for thebusbars even when the talking circuit is in operation and when thesignaling circuit is otherwise open these switches will close thesignaling circuit and operate the signals in all of the rooms connectedto the respective busbars as long as the program clock PC makes thebusbar contact. S2 indicates a solenoid switch associated with theprogram clock busbar contact 2 so as to operate the signected with thebusbar 3 when the program clock contact 3 is made although the apparatusmay otherwise be in position for operating the loud speakers byoperation of the switch MT3 or CA3 or CB3 etc.

20 indicates a device for bringing into the output transformer OT of apower amplifier or audio amplifier, radio set or phonograph the matter'which is to be distributed through various loud speakers. The device 20may therefore be taken to represent a microphone for direct speakingetc. or a phonograph for reproduction or a radio or telephone receivingcircuit or the like. The waves from the device 20 are received andsuitably transformed in the output transformer 0T for transmissionthrough the system by mechanism and arrangements well known in the artand therefore not necessary to be described in detail here. Theamplifier may be omitted if the source of audio energy is of sufficientpower to operate the loud speakers of the system.

' In order to clearly indicate the character of the invention the pathsand circuits of the apparatus will be described in such a way as toindicate the effects of the manipulation and operation of the variousswitches.

With the switches in the condition indicated on the drawing it will beseen that when the program clock has closed the contact 2 current willpass through the wire 2| to the lower contact 22 of the master talkingswitch MT2 to the switch arm 23 of that switch into the busbar 2 andthrough the plug A2? and through the wire 24 to the lower right handcontact 25 of the controlling switch CA2; through the switch lever 26the wire 21 to the lower left hand contact 23 and the left hand switchlever 29 through the wire 30 to the signal mechanism II in the room A2and by the wire 3| to the negative side of the battery. At the same timecurrent will pass from the busbar 2 through the plug B2P and the wire 32to the lower right hand contact 33 of the controlling switch CB2 throughthe right hand switch arm 34 and the wire 35 to the left hand contact 36and the left hand switch arm 31 and by way of the wire 38 to the signalmechanism IS in the room B2 which is connected to the return wire 3|. Ina similar way the closing of the contact 3 on the program clock PC willcause the signals l3 and H in the rooms A3 and B3 to be operated throughthe switches C'A3 and CB3.

When it is desired to operate the loud speakers controlled by busbar 2such as A2 and B2 the master talking switch MT2 may be operated so as toplace the switch arm 23 in contact with the upper contact 39. Thiscauses current from the output transformer OT to pass through the wire40 to the right hand contact 4| of the switch 7 S2 through the switcharm 42 and by the wire 43 to the contact 39 of the switch MT2 andthrough the switch arm 23, which is now in contact with 39, through thebusbar 2 to the plug A2? and through the wire 24, the contact 25, thearm 26, the wire 21, the contact 28, the arm 29 and the wire 30 to theloud speaker |2 the other side of which is connected. through the wires3| and 44 to the output transformer OT completing the circuit. At thesame time current will go from the busbar 2 through the plug B2P and thewire 32 to the contact 33, the arm 34, the wire 35, the contact 36. Thearm 31 and the wire 38 to the loud speaker I6 in the room B2 whenceconnection is made through the wires 3| and 44 to the output transformerOT.

In like manner the switch MT3 may be thrown to connect the talkingcircuit to the loud speakers the talking current normally operate thebell or signal mechanism.

It will be noted that in moving the arm 23 of the switch MT2 intoengagement with the contact 39 it has been lifted from engagement withthe contact 22. The opening at 22 breaks the signaling circuit for thebusbar corresponding to the contact 2 as described above. In order toallow for the time signal when demanded by the operation of the programclock PC the solenoid switch S2 has been provided. When the contact 2 ismade on the program clock PC current will come from the battery it bythe wire 2! to the contact 2 and will pass by the wire through thesolenoid S2 and by the wires 35 and 24 to the negative side of thebattery. This will energize the solenoid of the switch S2 so as toattract the switch arm 42 to the contact 4? thus for the time beingbreaking the talking circuit at the contact M. The talking circuit willthus remain open for the short time that the contact 2 is made on theprogram clock. The closure at the contact 4'! in the switch S2 providesa path from the positive side of the battery through the wires 2! and2-5 to the contact 4? and the switch lever 22 through the wire 43 to thecontact 29 of the switch MT2 and the switch arm 23 to the busbar 2 andthence through the plug AZP and the wire 24 to the contact 25 of thecontrolling switch CA2; through the switch arm 29, the wire 21, thecontact 28, the switch arm 29 and the wire 3i] to the signalingmechanism l i and through the wire M to the negative side of thebattery. The signaling mechanism iii in the room B2 will be energized atthe same time. The energization of the signaling mechanism will continueas long as the contact 2 is made by the program clock PC and when thatcontact is broken the signaling circuit will be broken and the talkingcircuit restored by deenergization of the solenoid of switch S2 allowingthe switch arm 42 of the switch S2 to return to the contact 4!. Each ofthe busbars may be provided with similar mechanism. The master talkingswitch MT3 and the solenoid switch S3 associated with the busbar 3 havebeen illustrated and it will be observed that they may be operated toclose the talking circuit for the instruments connected with the busbar3 and allow that circuit to be opened and the signaling circuit closedduring the short time when the program clock PC closes its contact 3.

Normally the switches may all lie in the positions indicated in thedrawing. It may be desired, however, to operate the signals in some orall of the rooms by manual means and this is provided for in thecontrolling switches exemplified by CA2, CB2, CA3, CB3, it beingunderstood of course that similar individual switches may be providedfor the apparatus which is located in each room of the school or otherbuilding. In order to energize the signal il in the room A2 the switcharm 29 of switch CA2 may be moved from the contact 28 to the contact 48.In this condition current will pass from the positive side of thebattery l9 through the wire 2! to the wire 49, to the contact 48 of theswitch CA2 through the switch arm 29 and the wire 30 to the signalmechanism l l which is connected to the negative side of the battery it)by the wire 3!. It will be observed that this operation of the lever arm29 of the switch CA2 will have no effect upon apparatus in any of therooms other than the room A2. Since. the talking circuit to the room A2when in operation passes through the contact 28 and the switch arm 29 ofthe switch CA2 it is obvious that upward movement of the arm 29 tooperate the signal mechanism II will break the talking circuit at thecontact 28 which may be remade when the arm 29 returns to its normalposition on the contact 28.

It will be remembered that the master talking switch MT2 connected thetalking circuit to all of the loud speakers connected with the busbar 2.Provision is made in the individual control switches CA2, CB2, CA3 etc.to energize the loud speakers in individual rooms without at the sametime energizing all speakers connected with the same busbar. Forinstance, the switch arm 26 of the control switch CA2 may be broughtinto contact with the contact 59 at the right of the switch CA2. In thiscondition a circuit will be closed from the output transformer OTthrough the wire 59 to the contact M of the switch S2, the switch arm 42the wire 63 and the wire 5| to the contact 59 and through the switch arm26 and the wire 21 to the contact 28, the switch arm 29 and the wire 39to the loud speaker E2 the other side of which is connected through thewires 3! and 54 to the output transformer OT. It will be noted that whenthe switch arm 26 is thus thrown to complete the individual talkingcircuit it does not interrupt the circuit through the solenoid of switchS2. Thus when the talking circuit through the loud speaker i2 iscompleted by contact of the switch arm 29 with the upper contact 59 theswitch S2 remains free to operate. the signal mechanism II when theprogram clock PC closes its contact 2. When this happens the solenoid S2will be energized as before by current coming from the battery throughthe wire 2i and the contact 2 on the program clock PC the wire 45 to thecoil of the switch S2 and by the wires at and M to the other side of thebattery l9. At this time the circuit for operating the signal II willcome from the battery l9 through the wire 2| and the contact 2 on theprogram clock PC through the wire 25 to the contact 41 of the switch S2through the switch arm 42, the wires 43 and 5! to the contact 59 throughthe switch arm 25 and the wire 21, the contact 28, the switch arm 29 andthe wire 39 to the signal device II the other side of which is connectedthrough the wire 3! to the other side of the battery It].

The details of the mechanism for throwing, operating and holding thevarious switches of the system forms no part of the present inventionand is not described since they are well known in the art. It will beobserved that the switches represented by S2 are so made that normallythe switch arm 42 engages the contact 41 and is drawn from such positionand into contact with 41 only while the coil of the switch is energizedreturning to contact with 4% when the coil is de-energized. In theseries of switches exemplified by CA2 the arm 29 is normally in contactwith 28 but may be lifted, preferably manually, therefrom and held incontact with 48 the arrangement being such that when it is released itwiH return to contact with 28. The switch arm 25 of the switch CA2 whileshown in contact with 25, which may be considered its normal position,may be moved into contact with 59 and preferably may be held or lockedinto that position and so remain as long as it is desired to maintainthe talking circuit closed. When the locking or holding mechanism isreleased the switch arm 26 should return to contact with 25. In theseries of switches exemplified by MTZ the switch arm 23 is normally incontact with 22 but may be moved and held or locked into contact with 39as long as it is desired to keep the talking circuit closed. When thelock or holding mechanism is released the arm 23 should return tocontact with 22.

A variation of the system may be made where alternating current is usedfor operating the bell or other signaling mechanism and this may consist of simultaneously applying both signaling and talking voltage orsuperimposing the signal ing voltage upon the talking voltage whensignaling is desired. The way such a system may be arranged and operatedmay be seen from the diagrammatic fragment indicated in Fig. 2 of thedrawings; Apparatus associated with two rooms only is indicated but itwill be understood that the apparatus may be duplicated and applied toas many rooms as necessary.

In Fig. 2, A represents the apparatus located for instance in the roomof a school comprising a bell or other signaling device 66 placed inparallel with loud speaker 6|. As a means of additional protection acondenser C may be placed in the branch containing the loud speakeralthough this is not essential and it may be omitted if aproperlydesigned loud speaker is used or it may be replaced by a currentlimiting resistor. PC represents the program clock. MT indicates a.master talking switch for the current associated with contact 2. At CAis represented a control switch for the apparatus A and at S isrepresented a solenoid signal switch. O'I represents the outputtransformer and AS represents a source of alternating current foroperat- 3 ing the bells or other signaling mechanism. The

switches are illustrated in their normal position to connect thebell-ringing or signaling system when the appropriate contact is made inthe program clock PC. The path of the current may be traced from thesource AS through the wire 62 and the contact 2 on the program clock PCwhich is connected to the busbar, through the plug AP and the wire 63 tothe contact 64 shown at the lower right hand side of the switch CAthrough the switch arm 65 and the wire 66 to the lower left hand contact61, the switch arm 68 and the wire 69 to the bell or signaling mechanism66 the other side of which is connected through the wires 16, H and 12to the source of I alternating current AS. It will be understood ofcourse that this circuit will be closed only at the prearranged timesfor which the program clock is set. It will be understood also as manyother local signaling apparatus as desired may be connected through andoperated from the busbar 2.

In order to transmit matter to the loud speakers 6| in the roomscontrolling the busbar 2 the master talking switch MT may be closed.This will close a path from the output transformer OT through the wires13 and 14 through the closed switch MT and by the wires 15 and 16 to thebusbar 2 and through the plug AP and the wire 63 to the lower contact 64in the switch CA through the switch arm 65 and the wire 66 to the lowerleft hand contact 61 and through the switch arm 66 and the wire 69 tothe loud speaker 6| the other side of which is connected to the otherside or" the output transformer OT through the wires 16, H and 11.

It will be noted that this talking circuit closed by the switch MT doesnot interrupt the signaling circuit described above. It will be obviousthen that with the master talking switch MT closed the program clock PCmay operate to close the signaling circuit and both signaling andtalking circuits will pass through the wire 69 into the apparatus in theroom A and by properly designing the apparatus and properly selectingthe character of the currents both loud speaker and signaling mechanismmay be operated.

It may be desired from time to time tooperate the signaling mechanism 66independently of the program clock PC and this may be done by manual orother operation of the switch arm 68 of the switch CA. By moving the arm68 away from contact 61 the talking circuit will be broken and when thearm 68 reaches the upper contact 18 it will close a signaling circuitfrom the source of current AS through the wire 19,

the contact 18, the switch arm 68 and the wire 69 to the bell orsignaling mechanism 66 the other side of which is connected through thewires 16, H and 12 to the other side of the current source AS. Theswitch arm 68 when released may return to the contact 61.

When it is desired to operate not all the loud speakers associated withbusbar 2 but only the loud speaker at A the switch arm 65 of the switchCA may be moved from contact 64 on to contacts 86 and 8| where it may beheld or may be locked into position for as long a period as it isdesired to operate the loud speaker. The talking circuit in thiscondition is from the output transformer OT through the wires 13 and 82to the contact 8|, the switch arm 65, the wire 66, the contact 61, theswitch arm 68 and the wire 69 to the loud speaker the other side ofwhich is connected through the wires 16, II and 11 to the other side ofthe output transformer OT.

It will be remembered that the signaling circuit controlled by theprogram clock PC as in dicated above passed through the contact 64 andthe switch arm 65. When the switch arm 65 is moved from contact 64 thiscircuit is broken. To provide for the operation of the signaling circuitunder the control of the program clock PC when the switch CA has beenthrown to close the talking circuit a solenoid switch S is provided.When the program clock PC makes its contact at 2 the signaling circuitfrom the source of supply AS passes through the wire 62, the busbar 2,the wire I6, the wire 83, the solenoid of the switch S the other side ofwhich is connected to the other side of the source of supply AS throughthe wires 84, H and 12. The energization of the solenoid of the switch Swill cause the switch arm 85 to engage the contact 86 thus closing acircuit for signaling current passing from the source of current supplyAS through the wire 62, the busbar 2, the wires 16 and 83 to the switcharm 85, through the contact 86 and by the wire 81 to the contact 86which is in engagement with the switch arm lever 65. The circuit thenpasses from the switch arm 65 through the wire 66, the contact 61 theswitch arm 68, the wire 69 to the signaling mechanism 66 the other sideof which is connected to the other side of the source of supply ASthrough the wires 16, H and 12.

It will be observed that when the signaling circuit is closed foroperation during the time the talking circuit is closed both circuitspass to the apparatus at the room A part operating the loud speaker andpart operating the signal mechanism arranged in parallel. The variouscomponents of the circuits and instruments may be so designed, installedand constructed that but a very small amount of the signaling currentpasses through the loud speaker and a very small amount of power fromthe output transformer is consumed by the signaling mechanisms. In thisarrangement the talking circuit is not interrupted for the operation ofthe signals.

The system has been described as comprising a signaling mechanism and aloud speaker at the various rooms or local stations controlled andoperated from the main central station which, as above indicated, may ormay not be the office of the principal. No means has been indicated atthe individual rooms for controlling or cutting in or out the mechanismbut obviously each portion or all of the apparatus in each room may haveassociated with it switches for connecting or disconnecting it with thesystem.

In many schools there is already installed a signaling system controlledmanually or by a program clock. The modern trend is to install inschools a central radio and announcing system so that from some centralpoint radio may be switched to any room or group of rooms through loudspeakers mounted in the individual rooms and the principal or others mayaddress one or more class rooms or the auditorium. Such programsstarting either from the auditorium or other points within or withoutthe school, or phonograph music or the like may be played through thevarious loud speakers. This has ;generally necessitated a secondcomplete wiring system to every room adding considerably to the expensein a new building and making sound installations practically prohibitivein old buildings. The present invention comprises an arrangement bywhich a sound system may be added without appreciable additional wiringeither in new installations or where old signaling systems are alreadyinstalled and at the same time in such a manner as to give the signalpreference at all times over the sound system.

It will be understood that satisfactory operation of the system isdependent upon the relation of the bell or other signaling mechanism andthe speakers and their circuits which must be such that the voltage andfrequencies required to operate the loud speaker at satisfactory volumewill not normally operate the signaling mechanism. The voltage or thevoltage and frequencies of the signaling circuit must be such that theywill not normally operate the loud speaker nor interfere with nor injurethe same.

The system may be varied in numerous ways, such as connecting severalbells in multiple with one loud speaker, or several speakers in multiplewith one bell, or in any combination desired. The master switch may bein one section, or there may be sub-masters for each program circuit.The system could be made to operate effectively by placing the loudspeaker in series with the bell leaving everything else practically thesame except for the proper adjustment of the operating voltages. Thereare of course many detailed variations which can be made in thesecircuits and still produce an operable system.

The invention has been disclosed in specific forms, but is not confinedto the details shown as it may be embodied in other arrangements and inother apparatus.

I claim as my invention:

1. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the individualsignaling mechanisms, means at a remote point for selectively operatingthe individual loud speakers, means at a remote point for selectivelyoperating a group of the signaling mechanisms, means at a remote pointfor selectively operating a group of the loud speakers, a program clockfor operating the signals at predetermined intervals, and meanscontrolled by the clock for interrupting the operation of the loudspeakers and operating the signaling mechanisms and subsequentlyrestoring the operation of the loud speakers.

2. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the individualsignaling mechanisms, means at a remotepoint for selectively operatingthe individual loud speakers, means at a remote point for selectivelyoperating a group of the signaling mechanisms, means at a remote pointfor selectiveiy operating a group of the loud speakers, a program clockfor operating the signals at predetermined intervals, and meanscontrolled by the clock for operating the signaling mechanisms when loudspeaker controlling mechanism isin position for operating the loudspeakers.

3. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the individualsignaling mechanisms, means at a remote point for selectively operatingthe individual loud speakers, means at a remote point for selectivelyoperating a group of the signaling mechanisms, means at a remote pointfor selectively operating a group of the loud speakers, a program clockfor operating the signals at predetermined intervals, and meanscontrolled by the clock for operating the signaling mechanisms when loudspeaker controlling mechanism is operated.

4. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the individualsignaling mechanisms, means at a remote point for selectively operatingthe individual loud speakers, means at a remote point for selectivelyoperating a group of the signaling mechanisms, means at a remote pointfor selectively operating a group of the loud speakers, a program clockfor operating the signals at predetermined intervals, and meanscontrolled by the clock for passing signaling current through the systemwhen loud speaker current is passing through the system.

5. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating signaling mechanisms,means at a remote point for selectively operating the loud speakers, aprogram clock for operating the signals at predetermined intervals, andmeans controlled by the clock for interrupting the operation of the loudspeakers and operating the signaling mechanisms and subsequentlyrestoring the operation of the loud speakers.

6. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the individualsignaling mechanisms, means at a remote point for selectively operatingthe individual loud speakers, a program clock for operating the signalsat predetermined intervals, and

means controlledby the clock for interrupting the operation of the loudspeakers and operating the signaling mechanisms and subsequentlyrestoring the operation of the loud speakers.

'7. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,

means at a remote point for selectively operating a group of thesignaling mechanisms, means at a remote point for selectively operatinga group of the loud speakers, a program clock for operating the signalsat predetermined intervals, and means controlled by the clock forinterrupting the operation of the loud speakers and operating thesignaling mechanisms and subsequently restoring the operation of theloud speakers.

8. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the signalingmechanisms, means at a remote point for selectively operating the loudspeakers, a program clock for operating the signals at predeterminedintervals, and means controlled by the clock for operating the signalingmechanisms when loud speaker controlling mechanism is in position foroperating loud speakers.

9. In a transmission system a plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the signalingmechanisms, means at a remote point for selectively operating the loudspeakers, a program clock for operating the signals at predeterminedintervals, and means controlled by the clock for passing signalingcurrent through the system when loud speaker current is passing throughthe system.

10. In a transmission system a, plurality of signaling mechanisms, aplurality of loud speakers each in parallel with a signaling mechanism,means at a remote point for selectively operating the individualsignaling mechanisms, means at a remote point for selectively operatingthe individual loud speakers, means at a remote point for selectivelyoperating a group of the signaling mechanisms, means at a remote pointfor selectively operating a group of the loud speakers, a program clockfor operating the signals at predetermined intervals, and meanscontrolled by the clock for operating the signaling mechanisms with theloud speaker controlling mechanism in any position.

HUGO COHN.

